Essentially all types of rubber, both natural and synthetic, and particularly rubbers formed from dienes are known to be susceptible to deterioration resulting from prolonged exposure to oxygen, ozone, light and heat. A great deal of effort has been expended by those engaged in the field of polymer technology to develop various antidegradants that will effectively inhibit the adverse effects of aging of polymeric compositions. In addition, much work has been done to discover new ways to prevent antidegradants from leaving polymer compositions by extraction, migration or volatilization. One particular area of concern deals with the antidegradants used in the tire industry where improvements in the tires have increased their serviceable life thus prolonging the exposure to the degradative effects mentioned above.
One approach to the problems of extraction and volatilization has been to use compounds of higher molecular weight such as those disclosed in U.S. Pat. Nos. 3,975,414 and 4,152,319. Another approach has been to use a polymerizable antidegradative monomer to form polymers containing the segmeric form of the monomer as an integral part thereof. Such an approach is disclosed in U.S. Pat. Nos. 3,658,769 and 3,817,916. Still another approach has been to graft a reactive antidegradant onto an existing polymer chain as disclosed in U.S. Pat. No. 4,155,955.
The focus in the latter two approaches has been on polymers of high molecular weights. High molecular weight polymer-bound antidegradants can have a limited range of application due to their mutual insolubility or incompatability with dissimilar polymers. In addition, antidegradant monomers can not be incorporated in those polymers where the antidegradant functionality destroys the polymerization catalysts.